85% fan area exhaust duct experiment

I started working on the design of a test bench for EDFs. I drew up an exhaust duct in ALibre, 3d printed it, and ran the fan. The duct has an outlet area of 85% of the fan area; as recommended by experienced aeromodellers for maximizing thrust. The fan used for this test is a 64 mm Haoye ducted fan I bought from Hobby King. The fan is coupled with a 3800 kV, 500W motor; also from Hobby king. Powering the unit is a 3 cell battery 15C 1700 mAh battery.

This fan without the exhaust duct draw 125W, with the duct on it drew 133W. For the test with the contracting exhaust duct mounted to the fan, it drew 17 A and the loaded battery voltage dropped to 7.8V. If the battery voltage drops to 7.8V, that means the fan rpm won't be as high as I expected. Adjusting my power draw predictions for this reduced rpm, due to reduced voltage, I'm over predicting by about 50%, which is bad, but better than being off by 600% when assuming full rpm. I need to continue working on this test bench to understand what the fan is doing. Measuring rpm will be useful.

The plan for the test bench is to measure differential pressure across the fan, rpm of the fan using IR phototransistor, and flow rate using pitot tube. I'm hoping that all these measurements will allow me to produce fan curves, experimentally.




Photo 1: Haoye 64mm EDF mounted to the base frame. Note that mounting the ducted fan with screws was a bad idea.




Photo 2: 3D printed exhaust duct with static pressure measuring nipple and pitot tube mount.




Photo 3: Exhaust duct with pitot tube.

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